Many conveying devices exist for transporting articles such as boxes. Some use flight bars, plates or other pushers that contact the conveyed boxes only from the rear to the thereby push the boxes along the conveying device. In other systems, boxes are gripped simultaneously from the front and rear as they are conveyed. The front and rear holders may be attached to separate endless loops, such as chains, which are driven at the same speed. A box is placed between a given set of holders and carried along the conveyor by the chains. The box typically enters and exits the conveyor at upstream and downstream ends where spacing between the given holders is larger, for example, as a leading or trailing holder travels out of a horizontal conveying plane and around an axle, making space for the box to be gripped by or released by the pair of holders.
Devices have been developed to adjust the spacing between holders on the two endless loops of such a conveyor to allow different-sized boxes to be securely conveyed. Such systems generally work well for their intended purposes but may require several adjustments to change box size. For example, if the relative position of only one endless loop conveyor and accordingly its holders is adjusted, the centerline of the articles being conveyed would change by half the amount of adjustment. Thus, although the pair of grippers would remain on pitch (i.e., spaced the same distance from each other), the timing of the conveying device would have to also be changed as compared to the rest of the system external to the conveying device. For example, both loops of the conveyor would have to be jogged forward or backward by a certain amount to synchronize with the timing of the system, typically by user input into a programmable logic controller or the like to drive servo motors to move both loops. Although such operation is effective, it adds steps and complexity to the adjustment process.
Accordingly, a secure, accurate, and simplified system for adjusting holders of endless loops on a conveyor that addressed one or more of the above issues, and/or that provided other benefits, would be welcome.